The use of force falls into two categories, generally. This is the use of force against the person, and the use of force against property. The use of force against a person is usually known as an assault. The use of force against property is usually known as wilful damage, or wilful destruction. Both are illegal unless authorised, justified, or excused, by law.

Where justified, or authorised, by law the use of force must be reasonable. This is an area where actions taken in an instant can be argued in a court for months. Reasonable use of force means it must be reasonable in the circumstances. It must be sufficient to overcome resistance, but not so great as to be deemed unreasonable, excessive, or reckless. If it results in an unforseen outcome, then it will be subject to judicial review, generally. Refer to case law such as 'eggshell skull' assault outcomes such as death or grievous bodily harm, and how forseeable it was. In most jurisdictions liability is still attached despite an inability to forsee the outcome.

Things to be considered include the level of threat, the parity or disparity between parties, and the ability to withdraw. For police often they have no ability to withdraw, given their role in the community. They are required to engage in actions to prevent injury to others, to preserve the peace, and to apprehend those who break the law. Therefore they are required to go forward where the more prudent would retreat. The bodyguard is generally required to retreat with their client, and find an alternate route, where practicable. They are there to protect the clients person, not to fight, unless necessary. A security guard is there to protect property, given that property often is not movable, they are less able to retreat.

For any use of force the force must be appropriate. A two metre, muscular, fit, 20 year old, black belt in multiple martial arts, may not be justified in knocking down a one metre tall, 70 year old lady, with a baton ... however, reverse the positions, and if use of force was necessary the use of a baton may be justified by the little old lady, because of the physical disparity. The question has two parts, was the force necessary, was the amount of force used reasonable? To look at 'necessary' was the force authorised, justified, or excused, by law?

Any use of force may result in injury, and a court case. If it necessary to use force, ensure it is proportionate to the threat, and write good notes.